The present invention relates to a piezoelectric element used as an actuator or a sensor for fine positioning, and its manufacturing method.
Recently, electromechanical elements such as micro-actuators are attracting attention. Such elements may realize very small and highly accurate component parts, and the productivity may be greatly improved by using a semiconductor process in the manufacture of same. Particularly, a micro-actuator using piezoelectric elements is now under development as an element for fine displacement of a scanning tunnel microscope and for fine positioning of a head slider of a magnetic disk recording and reproducing unit (hereinafter called a disk drive unit).
Conventionally, in a disk drive unit, a magnetic head for recording and reproducing information on a magnetic disk is mounted on a head slider and attached to an actuator arm. The actuator arm is driven by a voice coil motor (hereinafter called VCM) and positioned to a specified track position on the magnetic disk, thereby recording and reproducing information by the magnetic head. However, as the recording density is improved, it is now very difficult to assure sufficient accuracy in such a conventional method of positioning by VCM only. Accordingly, in addition to a positioning means by VCM, technical developments are now in progress to realize high-speed and highly accurate positioning by fine driving of a head slider with use of a fine positioning means using piezoelectric elements.
Thus, piezoelectric elements are expected to be applied in various ways. To meet the expectation, piezoelectric elements are required to be small-sized, able to render low voltage drive possible and to generate considerable displacement, and a method of manufacturing thin film is now examined for the manufacture of such elements. In a thin film manufacturing method, there are two major problems. The first problem is that in order to obtain a piezoelectric thin film having excellent piezoelectric characteristics, it is necessary to form the film on a substrate such as a silicon mono-crystalline substrate. Also, it is necessary to laminate piezoelectric films in order to obtain great piezoelectric displacement. Accordingly, such thin film is manufactured by using two sheets of substrate according to the following method. Piezoelectric thin film is first formed on each substrate, and then the piezoelectric thin films are bonded to each other. After that, one of the substrates is removed by etching, then the bonded and laminated piezoelectric thin film is exposed. After etching the exposed piezoelectric thin film to let it have a specified piezoelectric pattern, the other substrate is removed by etching, thereby manufacturing a thin film piezoelectric element. However, the laminated piezoelectric thin film is very thick and its etching is difficult, frequently causing electrical shorts.
The second problem, as described above, occurs because the manufactured piezoelectric element in final use is in a state of being completely separated from the substrate on which the film is formed. That is, since a thin film piezoelectric element manufactured by a thin film manufacturing method is very thin, if the thin film piezoelectric element is separated from the substrate, it becomes difficult to mount it on another substrate without damaging it, and impossible to set up an actuator for high mass-production.
With respect to the second problem, Japanese Laid-open Patent H11-26733 discloses a manufacturing method for making a transferring layer made up of a thin film device, such as thin film transistor array having reliable characteristics, on a quartz substrate or a heat resistant glass substrate, after which, the transferring layer is transferred onto a substrate which is inexpensive and excellent in impact resistance, thereby realizing a light-weight, hard-to-crack, and low-cost liquid crystal display unit. In this manufacturing method, the thin film device formed on a quartz substrate or a heat resistant glass substrate is transferred onto other substrate, and in order to easily separate the thin film device from the quartz substrate or the heat resistance glass substrate, it is necessary to firstly form a separative layer on the substrate. However, when a substrate with such a separative layer formed thereon is used, it is difficult to generate vertical orientation on the film surface in the case of piezoelectric thin film, and there arises a problem that good piezoelectric characteristics cannot be obtained.
The present invention is intended to solve the above problem. The object of the invention is to improve the reproducibility of shapes in etching of piezoelectric thin film and to prevent the generation of defects such as shorting between the electrodes holding the piezoelectric thin film in the manufacture of a thin film piezoelectric element with a two-layer configuration of piezoelectric thin film, in order to provide a thin film piezoelectric element which may assure low costs and high yield without variation in piezoelectric characteristics, and its manufacturing method.
A manufacturing method for thin piezoelectric elements of the present invention comprises
forming a plurality of first thin film patterns on a first substrate, wherein a first piezoelectric thin film is held between a first main electrode layer and a first opposed electrode layer on the first substrate, and at least a part of the first main electrode layer disposed at the first substrate side is larger in shape than the first piezoelectric thin film and the first opposed electrode layer;
forming a plurality of second thin film patterns on a second substrate, wherein a second piezoelectric thin film is held between a second main electrode layer and a second opposed electrode layer on the first substrate, and the second piezoelectric thin film, the second main electrode layer, and the second opposed electrode layer are nearly same in shape as the first piezoelectric thin film;
forming a plurality of structures, integrated by bonding the first thin film pattern and the second thin film pattern opposed and positioned to each other so as to be placed one upon another, and an insulating resin layer for protecting the structures;
selectively removing only the second substrate in order to expose the plurality of structures protected by the insulating resin layer;
etching said insulating resin layer into a shape that covers a peripheral portion of the structure except a part of the first main electrode layer;
forming a connecting electrode pad for connecting the first main electrode layer, the first opposed electrode layer, the second main electrode layer, and the second opposed electrode layer to external equipment; and
selectively removing only the first substrate.
By this manufacturing method, the steps of finishing the main electrode layer and the piezoelectric thin film into specified shapes can be individually performed in a state of being formed on the first substrate and the second substrate. Accordingly, in a step of wet etching, the shape of the piezoelectric thin film can be formed with good reproducibility. Also, in wet etching, it is possible to eliminate foreign matter that is liable to stick to side wall surfaces in dry etching, and to realize a thin film piezoelectric element which hardly causes electrical shorting trouble and is stabilized in characteristics. On the other hand, in dry etching, as compared with the case of etching piezoelectric thin film having a two-layer configuration, the reproducibility of pattern shapes is improved because only one layer is etched, and also foreign matter that sticks to side wall surfaces during etching can be greatly reduced, thereby realizing the reduction of electrical shorting trouble and the stabilization of piezoelectric characteristics.